The solar panels are both
lightweight and efficient.
The HB-SIA has a 208-foot wingspan and weighs
materials for the binder that makes the
electrodes. We also proposed a chemical
component for the electrolyte. With these
materials, Solar Impulse was able to im-
prove the energy density of the batteries
by 50 percent.”
The pilots also used more creative means
to utilize potential energy for the plane.
At the end of the day, the batteries are
full and the plane is at maximum altitude.
The setup allows for three to four hours of
gliding — no energy usage — followed by
eight hours of battery-powered flight.
challenge that goes hand-in-hand with conserving
“Weight was the obses-
sion throughout the whole
development phase. We
defined technical objectives
in terms of performance
and the development fo-
cused on how to meet these
objectives (mechanical, UV,
The wing spar, cockpit, engine housing and
equipment parts were all designed with weight
in mind. Materials for these structural elements
are ultra-light foams or advanced polymers
— mainly special polyamids, polysulfones, or
polyethers — that replace metal parts wherever
possible, says Michel.
Specifically, the wing spar is made from a
lightweight paper honeycomb between carbon
fiber and coated with aqueous solution poly-amide-imide for strength.
One downside to the solar plane is its construction reduces resistance to bad weather including cross winds, turbulence, rain or humidity, so the HB-SIA only flies in good weather.
“There is a low quantity of energy available
for propulsion. It has a wingspan to weight
ratio in which the wings are 63 meters for a
weight of only 1600 kg,” says Michel. “It is a
fully electrical plane, so it has to be protected
Keeping it light
Obviously, keeping the weight light was a huge
“During this project we learned that the best
source of renewable energy is just sparing
energy,” says Michel. “When we have only
limited amounts of energy available, we have
to use it in a smart way. This makes two ele-
ments key, lightweight and low speed.”
After a successful landing of the solar plane
at its final destination of JFK, the team will
continue working on the HB-SIB, a more robust
version of the HB-SIA, to take on a trip around
the world in 2014.